The general objective is to study the roles of transcriptional regulatory sequences in the control of gene expression during embryonic development and differentiation. The specific objectives are to identify and characterize transcriptional regulatory sequences associated with histone genes of Xenopus laevis and to identify and characterize the putative protein factors that interact with the regulatory sequences. Conventional in vitro nucleic acid manipulation methods will be used to construct mutant histone genes containing deletions, insertions, and rearrangements. Manipulated genes will be microinjected into Xenopus oocytes and their expression will be studied by electrophoresis of radiolabeled RNA. In vivo and in vitro assays will be set up for putative regulatory sequence-binding proteins. These assays will be used to examine the interaction of proteins with specific RNA sequences and to characterize the proteins involved.